1. Field of the Invention
This invention relates to rasp blades used for removing rubber from the carcass of a tire in order to prepare the carcass for retreading.
2. Description of the Prior Art
Prior to applying a new tread to a tire carcass, it is necessary to prepare the surface of the carcass so that it is substantially uniform and has the proper shape and condition for receiving the tire retread material. It has been customary for a number of years to use a rotating hub with a large number of rasp blades mounted on the hub for cutting and buffing the surface of the tire carcass to prepare such surface for receiving the retread material. Such rasp blades have been used in numerous configurations and shapes in the prior art.
The preferred rasp blades in use prior to the 1960's had negative rake teeth of generally triangular profile notwithstanding short-comings in life and performance, since positive rake had been found to cause dragging and tearing which was cumulative and uncontrollable. This apparently occurred since the tooth spacing and tooth tip angles employed in rasp blades with positive rake teeth had a stretching effect which, under moderate to heavy pressure, pulled the rubber into the path of oncoming teeth.
The break-through which enabled positive rake to be used came with blades having tooth sets oppositely directed wherein teeth with negative rake were interposed between those with positive rake. Examples of such prior art tire rasps are disclosed in U.S. Pat. Nos. 2,896,309, 3,082,506 and 3,680,185. The control resulting from these configurations enabled the rasps to perform effectively, with higher rate of tread removal and longer life.
The control provided by teeth oppositely inclined, as described above, stems from the proximity of the outer edge of the negative rake teeth to the leading edge of the positive rake teeth. The teeth are usually in the form of sets of four with two pairs of teeth facing at opposite angles of inclination to each other with recesses between the teeth. Other examples of such prior art tire rasps are disclosed in U.S. Pat. No. 4,747,194, and the prior art cited therein. The present invention is an improvement on the tire rasp blades disclosed in the above patent and departs from the concept of oppositely inclined teeth which has been the common trade approach to rasp blade construction.